Radio direction finder



Dec. 6, 1938. G. DAVIES ET AL 4 RADIO DIRECTION FINDER Filed Jan. 19, 1934 Gauze/'45.. 3

Y l 10 1% Orion,

Patented Dec. 6, 1938 UNETEB STATES angers smear orrics H. Orton,

Washington, D. 0.,

assignors to Washington institute of Technology, W2shington, D. 0., a corporation of Delaware Application January 19, 1934, Serial No. 707,400

7 Claims.

The present invention relates to radio direction finder systems and, more particularly, to systems of this type adapted to provide a course indication in accordance with the direction of an incoming radio frequency wave.

An object of the invention. is to provide a system of the type described which may be employed with a usual radio receiving device which may be tuned to any desired broadcasting station, whereby the direction finder system will provide an indication of the direction of an incoming wave from such broadcasting station.

Another object of the invention is to provide a radio direction finder system comprising a loop antenna, the opposite sides of which are alternately connected to ground, in order to modulate currents induced in the antenna system acting as a vertical antenna, whereby combined currents are produced which are utilized to actuate a course-indicating device.

Another object is to provide, in a radio direction finder system, synchronously operated means for alternately grounding the opposite sides of a loop antenna system and for alternately supplying to the opposite terminals of a course-indicating device currents resulting from the combination of received non-directional radiations and radiations received alternately in opposite sides of a loop antenna,

Another object is to provide, in a radio direc tion finder system, means for separately energizing the input and output switching circuits in order to prevent currents in the output circuit from impressing upon the incoming signal carrier modulations corresponding to currents in the output circuit.

Another object of the invention is to provide a radio direction finder system comprising means for separately adjusting the switching voltages applied to the input and output switching tubes.

Another object is to provide a radio direction finder system comprising means for adjusting the total eirective capacitance between each plate of the input switching tube and ground.

Another object is toprovide a radio direction finder system comprising means for effectively obtaining two separate switching voltages having identical frequencies and a definite phase relationship for operating the input and output switching tubes, thereby further eliminating modulation of the incoming signal carrier by the output currents.

Other objects and features of novelty will be apparent from the following description and the annexed drawing, it being expressly understood,

(Cl. 2501l) however, that the invention is in no way limited by such description and drawing, or otherwise than by the appended claims.

Referring to the drawing, in which similar reference numerals refer to like parts:

Fig. 1 is a schematic view of a radio direction finder system according to the present invention;

Fig. 2 discloses 'a modification of the system disclosed in Fig. 1;

Fig. 3 discloses a further modificationof the invention, and

Fig. 4 is a view showing a modified arrangement of part of the systems disclosed in Figs. 1 and 2.

Referring to the system illustrated in Fig. 1 of the drawing, it will be seen that a loop antenna I has been provided, the center point 2 of which is connected by a lead 3 to the grid l of an amplifying tube 5. The ends of loop antenna l are connected by leads 5, l to the two plates 8, 9 of a switching tube iii through leads I E2, the oathodes i8, E9 of the tube being connected to ground at 2B. A variable condenser i3 is connected across leads 6, l for the purpose of tuning loop I to a desired incoming signal. Either of leads 6 or I may be connected to ground as at It, through a variable condenser l l, the drawing showing line i as so connected for purposes: of illustration. The variable condenser I! is provided for the purpose of equalizing the capacities of leads 6, l to ground.

Means are provided by the invention for alternately connecting opposite sides of the loop antenna i to ground at so through the switching tube l8, and such means comprise an oscillator 20, the output terminals of which are connected to the terminals of the primary coil 2! of a transformer 22. Two secondary coils 23, M are provided, and the terminals of secondary 23 are connected to the plates 8, 9 of switching tube ll] through leads 25, 26 and inductance coils 21, 28. Lead 25 is connected to ground at 29 through a fixed condenser 36, while lead 26 is also connected to ground at 29 through fixed condenser 3|. Secondary coil 23 of transformer 22 is connected to ground at 29 through a lead 32 which is tapped to the center of coil 23.

Lead 3 which, with the loop antenna 8, provides a vertical antenna, is connected to ground as at 34 through a resistance 35. Such connection to ground is effected from a point 33 in, lead 3, which point is preferably selected near the connection of lead 3 to grid 4 of amplifying tube 5.

Means are also provided by the invention for ube it.

amplifying the combined currents induced in the loop antenna acting as such and the antenna system acting as a vertical antenna. Such means comprise the amplifying tube 5, to the grid 4 of which the lead 3 is connected, as described hereinbefore. The cathode of the amplifying tube 5 is connected to ground at Bl through a resistance 38. The plate 39 of the amplifying tube is connected through transmission line '56 and fixed condenser ll to one input terminal 42 of a usual radio receiving device 43. The shield grid 46 is connected to ground at 46 through lead ill and fixed condenser 48 and is also connected to a B-battery 49 through lead 59 and resistance 5!, in the usual manner. Lead 50 is connected to the plate 39 through an inductance coil 52.

Referring to the radio receiving device 43, it will be seen that the same is of the usual type for receiving radio-frequency broadcasting, and

as described hereinbefore one input terminal A2 thereof is connected to the plate 39 of amplifying tube 5, the other input terminal 53 being connected to ground as shown.

Means are provided by the invention for supplying the currents delivered by the radio receiving device to the opposite terminals of a cours indicating device, and such means comprise the leads ti l, 55, the one ends of which are connected to the output terminals 56, 5'! of the receiver 33, and the other ends of which are connected to the terminals of the primary 58 of a transformer 59. One terminal of the secondary coilfit is grounded, as shown, and is also connected by a lead 6! and resistance 8! to the cathodes 62, 63 of the output switching tube 64. The other terminal of the secondary coil 60 is connected by a lead l! to the center of the secondary coil 24 of transformer 22. The two plates 65, 66 of the output switching tube 541 are connected to opposite terminals of a course-indicating instrument 61, which may be of the zero-center milliammeter type, by leads '58, 59. A fixed condenser 10 is connected in shunt across the terminals of the course indicating device 8?, and a resistance fl is connected between the plates 65, 66, such resistance being connected to the B-battery 49 through a centeriap l2, whereby the plates 65, 66 are connected to the B-battery in the usual manner. The two grids '53, M of the switching tube 65 are connected by leads l5, 76 to the terminals of the secondary 24 of transformer device 22, whereby t o grids will be alternately energized.

the operation of the above-described system will be noted that the antenna system I acts not only as a loop antenna but also as a vertical antenna. Due to the vertical effect of the an tenna system a signal is impressed across resistor at all times, and such signal is not affected in any way by the input switching means. This is the only signal received when the axis of the loop antenna points directly toward the transmitting station. At other times, i. e., when the axis of the loop antenna varies from a position in which the axis thereof points directly toward the transmitting station, a signal is induced in the loop circuit which constitutes the loop antenna l, leads 6, 7, l4 and i5, and'tuning condenser 53. A portion of such signal induced in the loop circuit is impressed across resistor 35 due to the connection of lead 3 to the center tap of loop l and the alternate grounding of one side of the loop through the input switching Such alternate grounding of the sides of the loop is effected by the input switching tube ll], to the two plates of which are connected the terminals of the secondary 23 of transformer 22, the primary of which is connected to the output terminals of oscillator 20. It will be apparent that plates 8, 9 will be alternately swung positive and negative, and that when one plate is swung positive current is passed therefrom to the corresponding filament and from thence to ground at 2B. As plates 8, 9 are respectively connected to opposite sides of the loop I, it will be apparent that opposite sides of the loop will be alternately connected to ground at 26 through the input switching tube.

If it is assumed that the axis of loop I, and therefore the longitudinal axis of the aircraft or other mobile body on which the loop is mounted, is pointed to the left of the transmitting station to which the loop is tuned, the plate 8 is grounded, at that particular instant the phase relations between vertical effect voltage across resistor 35 and loop voltage across resistor 35 are such that these voltages add; then when plate 9 of input switching tube I is connected to ground by the alternation of the switching voltage, the loop voltage across resistor 35 will subtract from the vertical effect voltage across resistor 35. Consequently, the radio frequency voltage across resistor 35 will be modulated at the frequency of the switching voltage source and the percentage of such modulation is determined by the relative values of vertical effect voltage and loop voltage impressed across resistor and hence by the angle included between the axis of the loop and the direction of the incoming signal, being proportional to the sine of this angle.

When the axis of the loop is pointed to the right of the transmitting station to which the receiver is tuned, the phase of the radio frequency voltage induced in the loop is reversed and it follows that the phase of the modulation impressed upon the radio frequency voltage across resistor 35 is likewise reversed.

It will be seen from the above that a radio frequency voltage, modulated at the frequency of oscillator 2E! proportionally to the sine of the angle between the axis of the loop and the direction of the incoming signal is supplied to the grid a of amplifying tube by lead 3. The action of the amplifying tube is well-known and will not be described further. The output of the amplifying tube is supplied to one input terminal of the receiver 43, which is of any usual and well-known design.

The output of receiver 43 is passed through transformer 59 and consists of the total modulations impressed upon the received signal, including those impressed at the transmitting station and in the input switching circuit as described hereinbefore. Such receiver output induces a voltage in secondary 60 of transformer 59. The voltages induced in secondary 60 are fed to the center of secondary 24 of transformer 22 and divide at that point, the resulting voltages being impressed on grids 13, 14 of output switching tube 64 equally and in parallel, i. e., both grids are positive or negative with respect to the modulated signal at the same time. The switching frequency voltage induced in the sec ondary 24 of transformer 22 is also impressed on grids l3, E4 in such manner that one grid is swung positively while the other is swung negatively. Consequently there are two voltages of switching frequency impressed on the grids 13, 14, and at any particular instant these two voltages add on one grid and subtract on the other. Accordingly, the current through the two sections of output switching tube 64 are correspondingly unbalanced and a deflection of meter 6'? is therefore produced. The amount of this defiection is dependent upon the receiver output voltage at the switching frequency, hence upon the percentage modulation of the incoming signal at the switching frequency, which in turn, as explained hereinbefore, is dependent upon the sine of the angle between the axis of the loop and the direction of the incoming signal.

It will be apparent that if the axis of the loop points directly to the transmitting station, no voltages from the loop circuit will be impressed across resistor 35, and the only voltage across resistor 35 will be that due to the vertical effect of the antenna, which is not modulated, or other wise afiected, by the input switching frequency. Consequently, such voltages due to the vertical effect of the antenna will be passed through amplifier tube 5, receiver 43, transformer 59, and will cancel out in the grids i3, 14. Therefore, the only currents supplied to the opposite terminals of the meter 5? will be equal and in opposite directions whereby no deflection of the meter will be caused and an on-course indication will be given.

A modified form of the present invention is disclosed in Fig. 2 of the drawing and, referring to such figure, it will be seen that the radio direction finder system disclosed therein is substantially the same as that disclosed in Fig. 1 and described hereinbefore, in all respects except the method employed for causing synchronous operation of the input and output switching tubes. It will be noted that, in the system disclosed in Fig. l, the output of the oscillator 20 induces a voltage in each of the two secondaries 23, 240i the transformer 22, and that the plates 8, 9 of the input switching tube H] are energized from the secondary 23, while the grids 13, M of output switching tube 64 are energized from secondary 20. In this manner it is insured that the input and output switching tubes are synchronously operated. In the modification according to Fig. 2, the transformer 22 of Fig, 1 is omitted and the output terminals of the oscillator H30 are connected directly to the plates 10! and 502 of input switching tube I03, through leads WA, 105. The output terminals of the oscillator are also connected directly to the grids I05, 50'! of output switching tube I08 through leads W9, H0.

By reason of the direct connection of the plates of the input switching tube and the grids of the output switching tube to the oscillator I00, the synchronous operation of the two tubes is insured, such operation being of great importance for reasons outlined hereinbefo-re. Otherwise,

'the system disclosed in Fig. 2 is identical to that disclosed in Fig. 1 and its operation being the same, the system and its operation will not be further described.

A modified arrangement of part of the systerns disclosed in Figs. 1 and 2 is illustrated in Fig. 4 and, referring to such figure, it will be seen that instead of employing both the input switching tube i and the amplifying tube of Fig. l, a single diode-pentode tube 300 is employed, the same performing both the input switching and amplifying functions.

Referring particularly to Fig. 4 it will be seen that the input switching circuit comprises the leads 30%, 302, the same being connected to the ends of the loop antenna, and the plates 303, 304

of the tube 300 being connected respectively to such leads. An oscillator (not shown) is also conected to the plates 303, 304 through leads 301, 302, and the ground connection through such plates is established through cathode 305 which is connected to ground at 306. A tuning condenser 30! is connected between leads 30! and 302, and either of such leads is connected to ground at 308 through a variable condenser 309 for equalizing the capacities thereof to ground. The center point of the loop antenna is connected to grid 3l0 of tube 300 by lead 3|! which is connected to ground through resistance 3I2.

The above describes the input switching circuit according to the modified arrangement disclosed in Fig, 4 and it will be apparent that the operation of such input switching circuit is exactly the same as the operation of the similar circuit described in connection with Figs. 1 and 2. Accordingly, no further discussion of the operation of this input switching circuit will be given.

The circuit illustrated in Fig. 4 also comprises an amplifying circuit, the same comprising the suppressor grid 3|3 which is connected to a cathode 3 I 4, the grid 315 which is connected to ground through fixed condenser 3H5 and to a B-battery through resistance 3H and lead 3l8, and plate 3!!! which is connected to the B-battery through inductance 320 and lead 3|8 and to the usual receiving device through fixed condenser 32! and lead 322.

The input switching and amplifying circuit described above may be substituted for the similar circuits of the systems disclosed in Figs. 1 and 2, and the operation of such circuits is exactly similar. The circuit illustrated in Fig. 4 has the advantage, however, of employing only a single tube for both the input switching and amplifying circuits, while the systems illustrated in Figs. 1 and 2 each require two tubes to operate such circuits.

The present invention also contemplates the provision of a radio direction finder system comprising means for eliminating the night effects inherent in systems employing the loop type antenna. Such a system is disclosed in Fig. 3 of the drawing and, referring to such figure, it will be seen that the system comprises the vertical antennas 200, 201, which are loaded to resonance or partial resonance by means of loading coils 200, 205 and which are respectively connected to ground at 202, 203. The antenna circuits also include the primary inductance coils 200, 201. Wound in inductive relation to coil 206 is a secondary coil 208, the terminals of which are connected to the primary coils 209, 2E0 of a hybrid coil system 2! i, such primary coils having their other terminals connected to the terminals of a secondary coil 2l2 which is wound in inductive relation to the primary coil 20'! in the circuit of antenna 20L The end terminals of secondary coil 213 of the hybrid coil system are connected through leads 2-H, 218 and fixed condensers 2&9, 220 to the plates 2M, 2I5 of input switching tube 2l6, the cathodes 22!, 222 of which are connected to ground at 223. Either of leads 21?, H3 may be connected to ground at 224 through a variable condenser 225 for the purpose of equalizing the capacities of these leads to ground. 4

Connected to the center points of primaries 209, 2!!) of the hybrid coil system are leads 220, 221, the same being also connected to the input terminals of an artificial line or phase-adjusting system 228, the output terminals of which are connected to the terminals of one primary coil 229 of transformer 230. Connected to: the center point of the secondary 2l3 of the hybrid coil system is a lead 23!, to the other end of which is connected one terminal of a second primary coil 232 of transformer 239, the other terminal of primary 232 being connected to ground at 233. The transformer 239 also comprises the secondary 234, one terminal of which is connected to ground at 235, the other terminal being connected through lead 236 to the grid 23'! of amplifying tube 238.

Referring particularly to the amplifying circuit, it will be seen that the tube 238 includes the cathode 239 which is grounded at 249 through a resistance 24!, the plate 242 which is connected through lead 243 and fixed condenser 24d to one input terminal of a radio receiving device 245, and the screen grid 246, which is connected to ground at 240 through lead 24'! and fixed condenser 248, and to a B-battery 249 through lead 250 and resistance 25!. Lead 250 is connected to plate 242 through an inductance coil 252.

The output terminals of the radio receiving device 245, which is of usual type, are connected to the terminals of primary 253 of a transformer 254 through leads 255, 256. One terminal of secondary 251 of transformer 254 is grounded at 258, and is also connected through lead 262 and resistance 291 to the cathodes 259, 258 of output switching tube 26!. The other terminal of the secondary 251 of transformer 254 is connected to the center point of secondary 284 of transformer 282 through lead 298. The plates 233, 264 of the output switching tube are connected respectively to the opposite terminals of a courseindicating device 265 through leads 266, 261, a fixed condenser 268 being shunted across such course-indicating device, as shown. The plates 263, 264 are also connected to. the B-battery 249 through leads 266, 261, resistance 269 and lead 219 which is tapped to the center of resistance 269.

Means are provided by the invention for synchronously energizing the input and output switching tubes and such means comprise the oscillator 280, to the output terminals of which are connected the terminals of primary 28! of transformer 282, which also comprises the two secondary coils 283, 284. The terminals of secondary 283 are connected to the plates 2I4, 2!5 of input switching tube 2M5 through leads 285, 286 and inductance coils 281, 288, and secondary 283 is also connected to ground at 289 through center-tape 299. Lead 285 is connected to ground at 289 through fixed condenser 29! and lead 286 is connected to ground at 289 through fixed condenser 292. The terminals of the secondary 284 of transformer 282 are connected by leads 293, 294 to the grids 295, 296 of output switching tube 26!, and secondary 284 is connected to ground at 291 through center-tap 298.

In the operation of the above-described system it will be apparent that the antenna and hybrid coil system will provide both the effect of a vertical antenna and that of a loop antenna. It will be obvious that the antennas 209, 20!, primaries 299, 2!!! of the hybrid coil system, and leads 226, 221 will provide the effect of a vertical or open antenna system. The voltages induced in this open antenna system will constantly provide a voltage across primary 229 of transformer 238. It will also be obvious that the circuit comprising secondary 2!3 of the hybrid coil system and leads 2!'!, 2H3 will act as a loop antenna in that voltages will be generated in secondary 253 by an incoming Sig-- nal equivalent to the voltages induced in a loop antenna by a signal coming from the same direction. When the system is in operation each of the plates 2 l4, 2! 5 of the input switching tube 2l6 will be alternately swung positively and negatively by currents set up in the secondary 283 by oscillator 289, and if it be assumed that plate H4 is positive at any moment, then at that moment current will be passed from plate 2|4 to cathode 22!, and lead 2i1 and that half of secondary 2!.3 between plate 2! 4 and the connection of lead 23! to the secondary will be connected to ground at 223. At this same instant, if the ship or plane carrying the system is not headed directly toward the transmitting station to which the receiver is tuned, the voltage induced in the said half of secondary 2l3 will cause a current to flow through primary 232 of transformer 239 through lead 23!. It will be apparent that at the next oscillation of generator 280,.

239 which, at any particular instant, will be a combination of the vertical antenna effect voltage across primary 229 and the loop eifect volt age across primary 232 due to voltages induced in one-half of the equivalent loop antenna circuit as described hereinbefore. It will be noted that if the plane carrying this system is headed directly toward the transmitting station to which the receiver 245 is tuned, no eifective voltage will be induced in the secondary 2 l3 and consequently there will be no voltage across primary 232 of transformer 23!]. In this case the voltage induced in secondary 234 will be due solely to the vertical antenna effect.

The voltages induced in secondary 234 of transformer 23!] by primary 232 add to and subtract from the voltages induced in said secondary by primary 229 in the same manner as the loop antenna voltages were shown to add to and subtract from the vertical effect voltages across resistor 35 of Fig. 1 in the description of the operation of the circuit shown in that figure, thus impressing on the incoming carrier a modulation of a frequency equal to that generated by theoscillator 280.

From this point on the operation of the circuit is identical with that of Fig. 1, and need not be further described.

While we have described herein certain modifications and embodiments of our invention, it will be apparent to those skilled in the art that further modifications and improvements in the invention may be made without departing in any way from the spirit or scope of the invention, for the limits of which reference must be had to the appended claims.

What is claimed is:

1. A radio direction indicator comprising a loop antenna system, an oscillator, a primary coil connected to be energized by the output of said oscillator, a plurality of separate secondary coils inductively coupled to said primary coil, a circuit connected to one of said secondary coils and to said loop system for modulating currents received by said loop antenna system, a circuit coupled to and operable with said loop system detecting said combined currents, a course indicating device, and means for supplying said combined currents to said course indicating device, said means comprising means for supplying said combined currents to the center point of another of said secondary coils, a plurality of audio frequency valve paths 'each including a grid to each of which is connected one terminal of said last-named secondary coil, a plate in each of said valve paths, each of said plates being connected to one terminal of said course indicating device.

2. A radio direction indicator comprising an oscillator, a primary coil connected to be energized by said oscillator, a plurality of separate secondary coils inductively coupled to said primary coil, a loop antenna system, means connected to said loop system and to one of said secondary coils for modulating currents received in said loop antenna system, a circuit coupled to said loop system and providing the effect of a vertical antenna, said vertical antenna circuit providing means wherein currents induced therein are combined with modulated currents induced in said loop antenna system to thereby provide a combined current, means for amplifying and detecting said combined current, an output circuit comprising a tube having two grids each of which is connected to a terminal of another of said secondary coils, means for supplying said combined current to the center-point of said secondary coil, whereby said combined current is supplied in parallel to said grids, and a course indicating instrument connected between the plates of said tube.

3. In a direction indicating system a plurality of spaced vertical antennas, a plurality of coils coupled to said antennas, a circuit connected to said coils and operable to provide the effect of a non-directional antenna system, a secondary coil inductively coupled to said coils, a circuit including said secondary coil and operable to pr vide the effect of a directional antenna system, a local source of alternating current, a transformer comprising a primary winding connected to said local source and a plurality of separate secondary windings, a circuit connected to said directional antenna circuit and to one of said secondaries and adapted to modulate currents received in said directional antenna circuit, means for combining currents induced in said non-directional antenna circuit with modulated currents from said directional antenna circuit, means for amplifying and detecting said combined currents, the detected current having a frequency equal to that of the current produced by said local source, an amplitude dependent upon the deviation of a line joining the source of received waves and the midpoint of the vertical antenna array from a line perpendicularly bisecting a line joining the antennas, and a phase dependent upon the sense of said deviation, means for combining said detected currents with current from another of said secondary windings to provide output currents, and means for supplying said output currents tothe terminals of a course indicating device.

4. In a direction indicating system, a plurality of spaced vertical antennas, a plurality of coils coupled to said antennas, a circuit connected to said coils and operable to provide the effect of a non-directional antenna system, a secondary coil inductively coupled to said coils, a circuit including said secondary coil and operable to provide the effect of a directional antenna system, a local source of alternating current, a circuit connected to said directional antenna circuit and connected to be effected by current from said local source for modulating currents received in said directional antenna circuit, means for combining the resultant modulated signal from the directional antenna circuit with current induced in the said non-directional antenna circuit to provide combined currents, means for amplifying and detecting said combined currents, the detected currents having a frequency equal to that of the local source, an amplitude dependent upon the deviation of a line joining the source of received waves and the midpoint of a line joining the vertical antennas from a line perpendicularly bisecting the line joining the antennas, and a phase dependent upon the sense of said deviation, means for impressing said combined and detected currents on the grids of an output circuit tube, means for alternately energizing the circuits of said tube at the frequency of said local source, and means for supplying the output of said tube circuits to the terminals of a course indicating device.

5. In a direction indicating system, a plurality of spaced vertical antennas, a plurality of coils coupled to said antennas, a circuit connected to said coils and operable to provide the effect of a non-directional antenna system, a secondary coil inductively coupled to said coils, a circuit including said secondary coil and operable to provide the effect of a directional antenna system, a local source of alternating current, a transformer comprising a primary winding connected to the output terminals of said local source and a plurality of secondary windings, a circuit connected to said directional antenna circuit and connected to be affected by current from one of said secondaries for modulating currents received in said directional antenna circuit, means for combining the resultant modulated current from the directional antenna circuit with the current induced in the non-directional antenna circuit, means for amplifying and detecting said combined currents, means for impressing said detected currents on another of said secondaries, means for impressing current from said local source and said detected currents on the grids of an output circuit tube, and means for supplying the output of said tube to the opposite terminals of a course indicating device.

6. In a direction indicating system, a plurality of spaced vertical antennas, a plurality of coils inductively coupled to said antennas, a circuit connected to the midpoints of said coils and operable to provide the effect of a non-directional antenna, a secondary coil inductively coupled to said coils, a circuit including said secondary coil and operable to provide theeffect of a directional antenna, an oscillator, a transformer having a primary coil connected to the output terminals of said oscillator and a plurality of secondary coils, a circuit connected to said directional antenna circuit and connected to one of said secondary coils for modulating currents received in said directional antenna circuit at the frequency of said local source, means for combining currents induced in said non-directional antenna circuit with the resultant modulated current from said directional antenna circuit, means for amplifying and detecting said combined currents, a course indicating device, means for supplying said detected currents equally to the grids of an output circuit tube, the plates of said tube being connected to opposite terminals of said course indicating device, said grids being connected to the output terminals of one of said secondaries, whereby said combined and detected currents are alternately added to and subtracted from current from said local source on the grids of said output tube, whereby a resultant course indicating current is supplied to the terminals of said course indicating device.

7. A radio direction indicating system comprising a vertical antenna array, a circuit 00- operating with said array to produce currents having the characteristics of currents induced in a directional antenna, a circuit co-operating with said array to produce currents having the characteristics of currents induced in a. nondirectional antenna, a local source of alternating currents, a circuit for modulating currents received in said first-named circuit, means for producing from the currents produced by said circuits resultant currents having the frequency of the local source, amplitudes dependent upon the deviation of a line joining the center of said array and the source of received radiations from a line perpendicularly bisecting a line joining the antennas of said array, and a phase dependent upon the sense of said deviation, a course indicating device, an output switching circuit for alternately supplying said resultant currents to the terminals of said course indicating device, and separate means separately energized by said local source for separately energizing said modulating circuit and said output switching circuit.

GOMER L. DAVIES.

WILLIAM H. ORTON. 

